Because Regiments never fought as Regiments, but as
individual Battalions, these Battalions had to be attached to larger formations
on the battlefield so that some degree of Command and Control could be exercised
over them. In the British Army in WW1 the basic formation was the Division, made
up of three Brigades.

Commanded by a Brigadier General, he had a staff of
officers and men which made up his Brigade Headquarters. With four Battalions
under his command, the War Establishment of the Brigade was more than 4,000
officers and men.

Brigades were normally numbered (eg. 12th Brigade),
but in the Territorial Force (T.F.) they were usually named. For example the 5th
and 6th T.F. Battalions South Staffordshire Regiment, and 5th and 6th T.F.
Battalions North Staffordshire Regiment together formed the Staffordshire
Brigade.

On the outbreak of war some Brigades were
temporarily disbanded, particularly in the T.F. The Battalions were often sent
overseas, and attached to existing Brigades in France for training. This meant
that in 1915 some Brigades had five Battalions. By 1916, most T.F. Brigades had
been reformed and the majority of Brigades were back to four Battalions.

In February 1918 the whole British Expeditionary
Force was re-organised. Lack of re-enforcements meant that it was no longer
practicable to maintain four Battalions. Therefore one was disbanded, and
Brigades thereafter were comprised of three Battalions, and organisation that
remained in use to beyond WW2.

Infantry Divisions

The Division was the main fighting formation on the
battlefield.

Commanded by a Major General, he and his Staff of
15 officers and 67 men controlled three Brigades, each of four Battalions.
Because a Division was a self-sufficient fighting force, it did not just
comprise of infantry. In addition to the three Infantry Brigades there were:

Artillery: three
Royal Field Artillery Brigades, a Howitzer Brigade, a Heavy Battery of the
Royal Garrison Artillery and a Divisional Ammunition Column, which supplied
the artillery brigades with their shells.

Engineers:three Royal Engineer Field Companies.

Divsional Train: nothing
to do with steam engines, this was the Division's transport, comprising
three Companies from the Army Service Corps.

Medical:
three Field Ambulances from the Royal Army Medical Corps.

Veterinary: because
most transport was horse drawn, there were Veterinary Sections from the Army
Veterinary Corps.

There was also a Divisional Signal Company of the
Royal Engineers, plus Mounted Troops and a Cyclist Company.

These units combined would make the strength of a
Division more than 18,000 officers and men.

As the war progressed, Tactical requirements on the
battlefield meant that the composition of a Division changed regularly. In the
Infantry Brigades from early 1916 onwards there was a Machine Gun Company of the
Machine Gun Corps, and a Trench Mortar Battery equipped with 2-inch Stokes
mortars.

At Divisional level, there were many changes and
additions. The Heavy Artillery units were removed in early 1915. Heavy Trench
Mortar Batteries, manned by Royal Garrison Artillery personnel, were added by
the time of the Somme in 1916. Labour units were added from 1916, including a
Divisional Pioneer Battalion (a former infantry Battalion converted to pioneer
status). A fourth Machine Gun company was attached to every Division from April
1917. A Divisional Employment Company was formed in every Division in May 1917.
In February 1918 the now four Machine Gun companies were amalgamated to form a
Divisional Machine Gun Battalion, which took the number of the Division (eg. 5th
Division had a 5th Battalion MGC).

This meant that by 1918 although a Division on
paper was now smaller in terms of manpower (16,000 men instead of 18,000 in
1914), it had more co-rdinated artillery support from field guns and mortars,
and more than 400 machine guns (Vickers and Lewis) instead of the 24 in August
1914.

By the close of the War there were 75 Divisions in
the British Army. Many had never seen service outside of England. Of this total,
12 were Regular Army, 30 were Territorial Force, 30 New Army (war time raised
Divisions), 1 Royal Naval Division and 2 Home Service Divisions.